Orphagen has identified antagonists to an orphan receptor that regulates the major biosynthetic steps of steroid hormone synthesis in the adrenal cortex and gonads. Safe and effective inhibition of adrenal steroid synthesis has a number of potential applications in oncology, including treatment of two rare and very poorly managed conditions. One is life-threatening, uncontrolled glucocorticoid and/or mineralocorticoid release from metastatic adrenocortical carcinoma (ACC). The other is Cushing's syndrome resulting from unresectable ACTH-secreting tumors that stimulate adrenal steroid synthesis without normal hypothalamic feedback. In addition, these novel orphan receptor antagonists are potentially of significant value in the treatment of hormone-dependent prostate cancer as chemical castration does not block release of the adrenal androgens, DHEA and DHEA-S, which contribute significantly to the total androgen load in prostate. The novel approach of specifically antagonizing this critical orphan receptor has the potential to be both safer and more effective than mitotane, ketoconazole and aminoglutethimide, broad spectrum P450 inhibitors currently used for this purpose. We propose in Aim 1 to characterize inhibition of steroidogenesis by receptor antagonists in cultured adrenal carcinoma cell lines and in primary adrenal cultures, confirming that the antagonists suppress steroidogenesis in cancerous and normal adrenal cells. In Aim 2, we plan to synthesize a metabolically stable tool compound for animal studies by modification of current antagonists, and in Aim 3 we propose to characterize the action of these on adrenal steroidogenesis in mouse. Proof-of-principle studies demonstrating overall efficacy of the novel antagonists for suppression of adrenal steroidogenesis will provide the framework for further preclinical development as well as the investigation of preclinical models, such as steroid secretion by adrenocortical cancer cell lines, adrenal activation by ACTH-secreting tumors, and regulation of adrenal androgen production in a non-rodent species. PUBLIC HEALTH RELEVANCE: Abnormal and excessive adrenal steroid production, producing severe abnormalities of metabolism or hypertension, threatens the lives of several thousand cancer patients/year. Steroids derived from the adrenal gland also contribute to the spread of prostate cancer, which causes more than 30,000 deaths per year in the U.S. Available therapies are not adequately effective. We have identified small molecule antagonists to a novel receptor that exerts broad control over adrenal steroid synthesis. Successful clinical development of these antagonists could markedly improve clinical prognosis for these indications.